Join Susan as she obsesses about cosmetic chemistry and other things (some possibly related to monkeys). Often strange, occasionally useful, and always worth a stop as a point of interest on your journey through the Intertron.

Tuesday, July 29, 2014

More questions about preservatives! Is citric acid a preservative? And how much preservative should I use?

There are loads of you with loads of questions about preservatives, so let's take a look at some of those comments now!

HOW MUCH PRESERVATIVE SHOULD I USE?
In this post, Question: Why would you leave preservatives out for sensitive skin?, Mariena asks: I use Phenonip in my lotions and emulsified scrubs and was wondering about the 0.5 to 1% usage rate. How do I know when to use just 0.5 and when to use 1.0% Perhaps in an anhydrous product, I could use 0.5 and in a lotion containing water, use 1%? What do you think?

When it comes to preservatives, I tend to err on the side of caution and use the maximum allowed because I can't be sterile in my workshop (but I do my best to be very clean). You'll notice in my recipes I always use the maximum allowed for Liquid Germall Plus because I don't know how you will make the products at home, and I'm hoping that using the maximum will cover you for all possible problems.

Having said this, like Liquid Germall Plus, Phenonip is a very good broad spectrum preservative, so it will do a great job at protecting your products at lower levels. If you're using hard to preserve ingredients - like our botanicals - then I'd go with the higher levels. If you aren't using a lot of botanical ingredients, then consider using a lower level. It really is up to your judgement how much you wish to use.

As an aside, you do not need to preserve products that are anhydrous - meaning they don't contain water - that won't be coming into contact with water. Products like whipped butters, lip balms, balms, sera, and so on don't need preservatives. You could use an anti-oxidant like Vitamin E to retard the rancidity of the oils, if you wish. Sugar and salt scrubs require preservatives because they are coming into contact with water when you put your wet hand into them when using them at the sink or in the tub or shower.

IS CITRIC ACID A PRESERVATIVE?In the same post, La Prairie Lady asks: I saw a lot of recipes with citric acid in water. that help ?? or just a light preservative for 1 month in the fridge.

Citric acid (or 2-hydroxy-1, 2, 3-propanetricarboxylic acid) is a chelating, anti-oxidizing, and pH altering ingredient that can bind metal ions, help prevent rancidity, and alter the pH of our lotions and surfactant mixtures. It is not a preservative that can prevent contamination from mold, yeast, and bacteria in our products.

Rancidity is a natural process in which our oil based ingredients degrade over time by being exposed to heat, light, and oxygen. It is inevitable, and while we can add anti-oxidants to our products to slow down the process, but we can't stop it completely. Citric acid can behave as a water soluble anti-oxidant in our products.

When citric acid is used as a chelating ingredient, it binds metal ions like calcium, magnesium, copper, zinc, nickel, and cobalt to keep our products from experiencing auto-oxidation. By binding these metals, it also keeps surfactant mixes nice and clear, and it helps to boost the efficacy of your preservative.

As an aside, you may see citric acid listed as a "natural preservative" for foods. This does not mean it is an effective preservative for cosmetics, and it is not approved as a broad spectrum preservative for our products. You might see it in combination with other preservatives, but generally it's being used as a chelating or anti-oxidizing ingredient.

If you're going to use a preservative, use it at the proper usage levels. As you can see from Liquid Germall Plus, the suggested usage rate ranges from 0.1% to 0.5%. Find something like this and use the lower level. If you use the lower level, you don't need to put it in the fridge - you can leave it out and use it like you would any other product.

HOW MUCH PRESERVATIVE SHOULD I USE IN A SUGAR SCRUB?

In this post, Formulating for your skin type: Emulsified scrubs for dry skin, Candice asks: When calculating the amount of preservative, should the weight of the sugar be included? If I make 100gr of scrub and add 140gr of sugar, do I include my preservative (1% optiphen in my case) as 1% of 240gr or 1% of 100% (only the emsulsion part, pre-sugar)?

You don't need to preserve the sugar or salt in a scrub, just the base of oils and other ingredients.

6 comments:

Do you think it is appropriate to always add a little citric acid with water in our recipes lotion and cream to delay rancidity without affecting the synergy of the other ingredients. I saw 1 teaspoon citric acid for 1 cup water.

Imo, also take into consideration the packaging when determining the preservative concentration. For jars, I always use the maximum amount because so much of the product is exposed to whatever microscopic beasties are on our fingers and in the air every time the jar is opened, plus whatever water, dirt and grime manage to find their way into the jar before it's closed. For sprays and pumps, I usually add a medium-range of preservative, unless the formula is predominantly hydrous ingredients and botanicals, then I add a bit more because those tend to be highly susceptible to contamination. For airtight containers, I add the minimum, unless I'm uncertain of some part of my process that day and then I'll add a bit more. I can't tell the skin-feel difference between 0.5% phenonip and 1.0%, but I do like knowing that I didn't risk wrecking an entire bottle (and possibly applying staph bacteria to my face) because I skimped on the preservative.

Hi La Prairie Lady. I cannot stress enough how much we want to use percentages and weights for our recipes. In theory - and only in theory - this would be 5 ml for 250 ml or 2%, which is incredibly high for any product! This would throw your pH for quite the loop. Considering that 0.1% to 0.2% in some recipes can alter the pH by 1 point, 2% would have a huge impact. (1/5 tsp would be 0.4% to give you an idea of how little you would need. Plus, a batch of lotion that used 250 ml would be upper limit of the batch size you'd want to make as a beginner!)

Please don't do this. And please measure with weights in the future because you are going to end up with some wacky non-working recipes that will be most frustrating!

Please don't use citric acid at all unless you have a good pH meter to measure the results because you could be putting some very very acidic things on your skin and can be hurt that way. I cannot stress this enough.

For beginning lotion makers, rancidity isn't that big an issue. If you are using long shelf life oils - more than 6 months - and making small batches - no more than 300 to 400 grams at a time - you won't encounter rancidity as your products will be well used by then! The only time you're going to encounter rancidity is if you're using oils that are about to go off - keep the dates on the containers so you know when you bought them or put them in the fridge/freezer when you're not using them - or when you're using grapeseed oil or unrefined hemp seed oil. If you are giving away your products to friends, put a best before date on them. If you're selling them...don't. You want to put at least two years into making products, and at least one year into testing each product you plan to sell.

So the short answer is don't worry about rancidity at this point in your formulating career.

I assure you, I have no intention of selling cosmetics, I just did for me. This is my new passion making soaps, creams and lotion, on the other side I am a veteran in naturopathic medicine for 35 years, I know the property oils and essential oils, plants ect. Now with internet all is so easy to learn something, no need to buy hundreds of books.

I ask questions because I believe that you have acquired a lot of knowledge in this domain.

I found on the net a young woman whose recipes ingredient have seemed logical, but she puts no preservative in its products but citric acid.

Hi Susan - I LOVE your blog. Rocky Mountain Soap claims there products are 100% natural. I questioned them on preservatives and they said their lotions contain either Vitamin E or Basil Oil (sodium levulinate) as the preservative. They also claim their lotions have been tested and are fine for up to one year. What are your thoughts on this?

Hi Michele! Thanks for your kind words. I'm glad you like the blog! I've tried to address your question in Wednesday, December 3rd's Weekday Wonderings. The short answer is that Vitamin E isn't a preservative, sodium levulinate is combined with sodium anistate in their products, and to say they are 100% natural is up for debate, in my humble opinion. Look for the complete post on Wednesday!

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Who the heck is Swift?

I'm an aspiring cosmetic scientician and DIY girl interested in pretty much any craft you can name - bookbinding, jewellery making, sewing, paper crafts, polymer clay - but my main passion is bath & body product making.
I am currently obsessed with Rock Band 3 (bass and singing) and science books. Did you know my favourite word is "toaster" and my favourite adjective is "hirsute"?
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